1. The Field of the Invention
The present invention relates generally to circuits used to convert electrical power into high voltage pulses. More specifically, embodiments of the present invention are directed to circuits for coupling a precise amount of power from a DC voltage source to a load, such as a pulse forming network or capacitor so as to allow for the formation of precision high voltage pulses for use by a variety of applications.
2. The Relevant Technology
A number of applications require the use of high voltage signal pulses. For example, various types of pulse forming networks or capacitors have been used to supply short duration, high voltage pulses to various types of loads, such as medical linear accelerator systems, magnetrons, and the like. In the past, one approach for charging such pulse forming networks has been to utilize a charge from a complex, high voltage DC source, such as a 10 kilovolt source, which is then connected to a step up transformer by way of a switch. However, such approaches have not been entirely successful in providing extremely precise output voltage values, a necessity in many precision applications. For example, additional circuits are often required to remove excess energy from the pulse forming network, which then must be dissipated. Such circuits are relatively inefficient, and also require a significant number of electrical components, which increases the cost and complexity of the overall circuitry.
An alternative technique is to utilize standard utility power to couple energy into the pulse forming network or capacitor. However, this approach also requires circuitry for coupling the energy from the low standard utility power into precision high voltage pulses. Unfortunately, the circuitry used in the prior art typically has a significant loss (i.e., poor efficiency) and/or requires elaborate and expensive energy recovery schemes to operate. Again, this increases the complexity and cost of the overall system. Moreover, typical approaches in the prior art utilize circuitry that is relatively limited in its operational range, and thus may not be entirely suitable for certain precision applications.
Consequently, there is a need for circuitry that is capable of converting standard utility power into precision high voltage pulses for use by pulse forming networks or capacitors. Moreover, it would be an improvement if such circuitry is efficient, provides a large operating range, and is relatively simple to implement and utilizes a minimal amount of circuit components. Also, it would be an improvement in the art to provide a coupling circuit that is capable of delivering a precise amount of energy to a load, such as a pulse forming network. Embodiments of the present invention address these and other needs.
In view of these and other problems present in the prior art, it is an overall objective of the present invention to provide an improved circuit and method for coupling energy from a voltage source to a pulse forming network or capacitor load. The circuit and method contemplated have ideal application in connection with high power modulator circuits, such as those that may be used in such applications and devices that include radar, accelerators, medical accelerators (e.g., klystron devices), pulsed lasers and the like.
By way of summary, embodiments of the present invention are directed to a coupling circuit that receives energy from a low voltage DC voltage source, and couples it to an energy storage load, such as a pulse forming network. In a preferred embodiment, electrical power is obtained from a standard utility power source having three phases of alternating current. The alternating current is converted to a direct current source using well known techniques.
Disposed between the DC voltage source and the energy storage load is a step-up charging transformer that receives energy from the DC source at its input winding, and provides at its output winding a significantly higher voltage, depending on the desired final voltage required in the energy storage load.
The output of the charging transformer charges the storage load through a charging inductor and charging diodes. In the preferred embodiment, a monitor circuit measures and monitors the current through the charging inductor and the voltage across the storage load. These voltages are utilized by a control circuit to continuously calculate and monitor the total combined energy of the charging inductor and the storage load, i.e., the total amount of energy within the circuit. When the total energy reaches a predetermined value, as indicated by a predefined reference signal having a specified voltage level, the control circuit causes a switching network, disposed between the DC voltage source and the charging transformer, to open. The switch circuit remains in an open, non-conducting state for a predetermined amount of time, corresponding for example to a desired pulse duration. During this open state, energy from the DC voltage source stops flowing into the circuit, and the energy stored within the charging inductor is transferred to the storage load via a conducting diode or any other appropriate circuit element. The pulse forming network or capacitor is then ready to be discharged into the corresponding modulator circuit. This process is then repeated for every charging cycle corresponding, for example, to each pulse generated into the connected device.
Preferred embodiments of the present invention provide several distinct advantages over the prior art. By providing a monitoring and control circuit that continuously monitoring the total energy delivered by the coupling circuit, the load voltage (and energy) can be maintained at a very precise and controllable value. This eliminates any need to remove excess energy from the pulse forming network, and thus increases efficiency and reduces the cost of the overall circuit. Also, since signals that are proportional to circuit energy are used to control and regulate the circuit""s operation, the circuit provide a very high degree of accuracy in controlling the load voltage. In addition, since the switches are opened at the point that the energy stored in the load and the energy stored in the inductor are substantially equal to the final desired energy, no unwanted energy is coupled into the circuit, again increasing the efficiency and accuracy of the circuit. The circuit also provides a minimal change in output energy, even with large variations of input DC source voltage.
These and other objects, features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.